1. Field of the Invention
The present invention relates to an inspection apparatus and an inspection method for obtaining information (physical properties, identification, concentration, presence or absence, and the like) of an inspection object by using an electromagnetic wave referred to as a so-called millimeter wave or terahertz wave of frequencies between 30 GHz and 30 THz (referred to as “terahertz wave” in this specification).
2. Description of the Related Art
In recent years, the technical development using a terahertz wave has been eagerly advanced. In particular, photon energy of the terahertz wave is comparable to energy of skeletal vibration of molecules or of interaction between the molecules. A technique using this terahertz wave is used to analyze a substance by using a spectrum and the like obtained by a spectroscopic method.
Under such technical situation, there is proposed a technique of analyzing DNA by utilizing the condition that terahertz wave propagation properties of a transmission line change when the terahertz wave transmission line is produced on a substrate, and a DNA water solution is dropped onto the transmission line and dried (APPLIED OPTICS/Vol. 41, No. 10, 2002, pp. 2074). This technique is studied because, by propagating the terahertz wave through the transmission line, it is possible to obtain an inspection apparatus which is reduced in size, is strong against an external environmental change, and can detect an inspection object of a very small amount. Further, this proposal indicates that, by utilizing the fact that a dielectric constant for the terahertz wave is different between a single chain and double chain of DNA, it is possible to inspect whether the DNA is made of the single chain or the double chain, in accordance with the difference of the terahertz wave propagation properties.
The configuration of this proposal has: a semiconductor thin film that functions as a photoconductive element; and a small functional device having transmission lines integrated on one substrate for propagating a generated electromagnetic wave. FIG. 7 shows a plan view thereof. In this configuration, there is provided a structure 164 obtained by transferring only a thin film of an epitaxial layer of a photoconductive element made of LT-GaAs onto a part of high frequency transmission lines 165 and 163 formed on a substrate 160. In this configuration, the structure 164 has such a structure that a micro strip line is formed on the Si substrate 160 so as to sandwich an insulator resin therebetween, a gap is generated in a part of the line, and the LT-GaAS thin film is arranged only below the gap. Driving is carried out such that a laser beam is emitted from a surface side of the substrate 160 through spatial propagation to gaps of metal lines 161 and 165, and the generated terahertz electromagnetic wave is propagated through the lines. On the transmission line, when an inspection object 167 to be examined is coated on a filter region 166 as a resonance structure, an EO crystal is used to detect a change in propagation state from a part 162. Thus, the physical properties of the inspection object 167 can be examined.
As mentioned above, the terahertz wave is used to determine optical properties, such as absorption coefficient and complex refractive index of a substance, from its change in the propagation state. Consequently, the analysis, detection, and identification of a substance can be executed. However, the method of APPLIED OPTICS, Vol. 41, No. 10, 2002, pp. 2074 does not use a special unit to drop the inspection object onto the transmission line with high controllability. Thus, it is not easy to drop the inspection object with high controllability in terms of the quantity and the position. That is, since the dropped liquid inspection object is apt to flow and spread, it is not easy to suitably control the position and amount of the inspection object for the transmission line.